The present invention relates to a compressor control apparatus and method for an automobile air-conditioning system, in particular, relates to an apparatus and method for controlling a compressor that is driven by an electric motor.
In an air-conditioning system having a compressor that is driven by an electric motor, as a capability of a heat exchanger is dropped when a discharge temperature of a refrigerant that is delivered from the compressor increases too much, an increase in the discharge temperature of the refrigerant that is delivered from the compressor is restricted. In the case of an air-conditioning system shown in the Japanese Patent Laid Open Publication No. 3-213956, a discharge temperature of a refrigerant that is delivered from a compressor is detected, and a revolution of the compressor is decreased by a prescribed revolution when a detected discharge temperature of the refrigerant is above a prescribed temperature. Hereby, an increase in the discharge temperature of the refrigerant that is delivered from the compressor is restricted.
If a revolution compensation of a compressor like this is applied to an automobile air-conditioning system of FIG. 4 that has an evaporator and a sub-condenser for heating in a car-room, a problem as described below may occur when an air-conditioning mode is a heating mode. That is, when a room temperature becomes 10.degree. C. or higher during the heating mode, a refrigerant pressure rises in a high-pressure side of the air-conditioning system even though a revolution of the compressor is decreased to cope with rise in a discharge temperature of the refrigerant, and the compressor is shut down by an operation of a pressure switch of the air-conditioning system. This is ascribed to reasons that a temperature of the air that flows into the subcondenser for heating is increased and that the subcondenser for heating cannot be scaled up in capacity in order to be provided in the car-room.
FIG. 4 shows an example of a conventional automobile air-conditioning system having an evaporator and a subcondenser for heating in a car-room. In FIG. 4, a reference numeral 1 is a compressor driven by an electric motor, a reference numeral 2 is an evaporator, a reference numeral 3 is a sub-condenser for heating, a reference numeral 4 is a main condenser for cooling, and a reference numeral 5 is a changeover valve. The compressor 1 at its suction port is connected to an outlet of the evaporator 2 via a refrigerant tube 6, and a delivery outlet thereof is connected to an inlet of the changeover valve 5 via a refrigerant tube 7. An inlet of the evaporator 2 is connected to an outlet of the main condenser 4 via a refrigerant tube 10 that has an expansion valve 8 and a receiver 9. The sub-condenser 3 at its inlet is connected to one outlet of the changeover valve 5 via a refrigerant tube 11, and an outlet thereof is connected to the inlet of the evaporator 2 via a refrigerant tube 13 that has an expansion valve 12. An inlet of the main condenser 4 is connected to the other outlet of the changeover valve 5 via a refrigerant tube 14. A reference numeral 15 is a discharge temperature sensor for detecting a discharge temperature of the refrigerant of the compressor 1. The discharge temperature sensor 15 is provided at the refrigerant tube 7 between the compressor 1 and the changeover valve 5. A reference numeral 16 is a pressure switch that operates when a refrigerant pressure in the high-pressure side of the air-conditioning system becomes above a prescribed high pressure value. The pressure switch 16 is provided at the refrigerant tube 13 between the subcondenser 3 and the expansion valve 12. The compressor 1 is shut down by an operation of the pressure switch 16. The evaporator 2 and the sub-condenser 3 are provided in a car-room 17, and the main condenser 4 is provided outside the car-room. A reference numeral 18 is a blower that is provided in the car-room 17. In a composition as described above, a heating operation and a cooling operation are carried out by switching the changeover valve 5. In the heating operation, a refrigerant path is formed, which begins from the compressor 1, passes through the changeover valve 5, the sub-condenser 3 for heating and the evaporator 2, and then returns to the compressor 1. In the cooling operation, a refrigerant path is formed, which begins from the compressor 1, passes through the changeover valve 5, the main condenser 4 and evaporator 2, and then returns to the compressor 1. In the heating operation, the air blown by the blower 18 is cooled by the evaporator 2 and then heated by the sub-condenser 3 for heating. Thereby, accordingly as the room temperature of the automobile rises, the air temperature rises in an air outlet side of the evaporator 2, that is, the air temperature rises in an air inlet side of the sub-condenser 3, and the refrigerant pressure rises in a refrigerant outlet or a high-pressure side of the subcondenser 3. As the sub-condenser 3 for heating is provided in the car-room, it cannot be scaled up in capacity. Thus, compared with the main condenser 4, the sub-condenser 3 easily increases the refrigerant pressure in the high-pressure side.
The conventional revolution compensation described above is applied to the automobile air-conditioning system of FIG. 4 so that the revolution of the compressor 1 is decreased by the prescribed revolution when the refrigerant discharge temperature is high. According to this, however, when the room temperature rises exceeding 10.degree. C. during the heating operation, a rise in refrigerant pressure in the high-pressure side is not restricted and it reaches the prescribed high pressure value, and thus the pressure switch 16 operates. To avoid this, the prescribed revolution mentioned above is increased in order to restrict the rise in refrigerant pressure in the high-pressure side, and the revolution of the compressor 1 must be decreased on a large scale when the refrigerant discharge temperature becomes high. According to this, however, when the room temperature is still low in the heating operation, a cold air is blown out due to a drop in the capability of the sub-condenser 3 for heating which is caused by a great decrease in revolution of the compressor 1, though the car-room has become warmed up, and thus a favorable heating cannot be attained.
Further, in the case of the automobile air-conditioning system of FIG. 4, as the compressor 1 is shut down by a rise in refrigerant pressure in the high-pressure side when the room temperature becomes 10.degree. C. or higher in the heating mode as described above, a maximum revolution of the compressor 1 is inevitably set lower to restrict the rise in refrigerant pressure in the high-pressure side. Thus, when the room temperature is low, the heating capability is inferior and a favorable heating cannot be attained.